Automotive refinish coating compositions have traditionally been based on low solids solvent-borne technology. This enables the use of high molecular weight resins and fast evaporating solvents, both of which enable rapid drying under ambient conditions thereby minimizing issues related to dirt pick-up and sag in the body shops. However, environmental legislation across the globe has resulted in the paint industry attempting to move towards greener and more ‘eco-friendly’ products with similar performance attributes as conventional coating formulations. Increases in the total solids content or a replacement of certain organic solvents by water are two alternatives available to the coating suppliers to limit the amount of volatile organic compounds (VOC) in the coating formulation.
High solids coatings have limited degree of film shrinkage owing to the reduced amounts of solvent whereas waterborne systems have relatively slow evaporation rates compared to standard organic solvents. Hence one of the challenges facing the automotive refinish coatings market is to tailor newer technologies (both high solids and waterborne) to achieve comparable degrees of aluminum flake control as observed in conventional solvent-borne low solids coating systems.
While waterborne refinish coatings do offer reduced Volatile Organic Content (VOC) emissions, there are several challenges associated with adopting this technology in a typical collision repair facility. These may range from modifying the air-flow in the spray booth to upgrading the spray equipment in order to specifically apply water based coatings. The additional provisions that are needed to equip the body-shops to spray waterborne paints would come with an increased level of capital investment. Therefore a performance additive that can enable the continued use of solvent-borne refinish coatings but at higher levels of non-volatile content will not only help reduce VOC emissions but also avoid conversion costs (to waterborne refinish coatings) and account for higher throughput due to the increased total solids in the coating composition.
This invention provides for the use of low molecular weight cellulose mixed esters in a refinish coating composition, which can raise the non-volatile content of the paint by 60% (when compared to conventional low-solids solvent-borne refinish coatings) and yet provide comparable performance to the traditional systems.
The automotive refinish coatings business in North America is under pressure to move to formulations that are lower in solvent emissions. A number of states have initiated a move to mandate the use of lower VOC coatings for automotive refinish applications. Therefore there exists an unmet need to develop refinish coating technologies with lower VOC emissions without compromising on the final performance attributes of the coating composition. The incorporation of low molecular weight cellulose mixed esters in a refinish coating formulation was found to increase the solids level in the paint by as much as 60% when compared to coatings that had similar amounts of conventional cellulose esters, such as, CAB 381-20 cellulose ester produced by Eastman Chemical Company, without causing any significant impact on the spray application viscosity. The low molecular weight cellulose mixed esters can be obtained from Eastman as Developmental Performance Additive (DPA) 2386. The increased levels of solid in the refinish coating composition can result in lower solvent emissions, thereby lowering VOC levels as well as improving the overall productivity of a repair facility by yielding excellent appearance properties.